Acoustic Higher‐Order Topological Insulators Induced by Orbital‐Interactions

Abstract The discovery of higher‐order topological insulator metamaterials, in analogy with their condensed‐matter counterparts, has enabled various breakthroughs in photonics, mechanics, and acoustics. A common way of inducing higher‐order topological wave phenomena is through pseudo‐spins, which mimic the electron spins as a symmetry‐breaking degree of freedom. Here, this work exploits degenerate orbitals in acoustic resonant cavities to demonstrate versatile, orbital‐selective, higher‐order topological corner states. Type‐II corner states are theoretically investigated and experimentally demonstrated based on tailored orbital interactions, without the need for long‐range hoppings that has so far served as a key ingredient for Type‐II corner states in single‐orbital systems. Due to the orthogonal nature of the degenerate p orbitals, this work also introduces a universal strategy to realize orbital‐dependent edge modes, featuring high‐Q edge states identified in bulk bands. These findings provide an understanding of the interplay between acoustic orbitals and topology, shedding light on orbital‐related topological wave physics, as well as its applications for acoustic sensing and trapping.